A device of the type referred to is known from EP 1 520 161 B1 and includes a clamp-type fixture having two clamping units which are floating-mounted relative to one another in the in-feed direction and movable relative to one another by means of a feed unit to increase or reduce their relative distance. The lower clamping unit includes holding electrodes for receiving corrective weights formed from sheet metal pieces, and the upper clamping unit includes counter-electrodes lying opposite the holding electrodes and having plane contact surfaces. For welding on a corrective weight, the upper clamping unit carrying the counter-electrode is moved towards the rotor. This is followed by an in-feed movement of the lower clamping unit, with the upper clamping unit serving as backing run. The corrective weight resting in its holding electrode is pressed against the rotor circumference from below and attached to the rotor by connecting the electrodes to a source of welding current.
Moreover, DD 235 584 A1 discloses a device for projection welding cup-shaped workpieces, which enables components to be welded to cup-shaped workpieces radially from inside. A component provided with two welding projections is carried in a holding electrode, and the cup-shaped workpiece is moved to a location above the component and aligned. In this arrangement, the holding electrode is attached to a swinging electrode carried on rollers in a spring-mounted guide frame. The guide frame is guided on an arm extension mounting at the same time a contact electrode making engagement with the swinging electrode with the device in operation. In addition, the arm extension is urged in the direction of effect against an upper electrode by means of a spring biased by an adjusting screw.
In the welding of corrective weights by means of a device of the type referred to, a variety of problems may occur. In the area of the counter-electrode resting against the rotor, the rotor may experience inadmissible deformations caused by the pressing force and the effect of the welding current, and the counter-electrode may be subject to premature wear requiring its frequent replacement. When corrective weights provided with several welding projections are welded on, it may happen that the welding current is unevenly distributed in the individual welding projections, possibly resulting in the corrective weight being insufficiently anchored to the rotor.